Phenomenology is treated ambiguously in McLuhan’s posthumous Laws of Media, which was edited and co-authored by his son, Eric. On the one hand, it is seen as an abstract attempt¹ to achieve what could not, in McLuhan’s view, be achieved in this way:

the root problem of phenomenology [is] that it is an all-out attempt by dialectic to invent — or turn itself into — grammar, to force some sort of ground to surface. (10-11)

Phenomenology is dialectic in ear-mode — a massive and decentralized quest for roots, for ground. (62)

From Hegel to Heidegger, phenomenologists have engaged in an attempt to get at the hidden properties or hidden effects of language and technology alike. In other words, they have tackled a right-hemisphere problem using left-hemisphere techniques and modes of cognition. (126)

On the other hand, phenomenology is seen, at least in Heidegger, as anticipating, however abstractly, just the sort of investigation that McLuhan himself was attempting:  

Heidegger’s language (…) in the German (…) is witty and concise, and his discussions pay close attention to the play of etymologies in [the] terms [he employs]², in an evident attempt to retrieve grammatical stress as a new mode of dialectic (…) [His work amounts in this way to] a special technique of perception that reveals the ground.³ Since ‘the actual’ emerges as a figure from the ground of [a] ‘standing reserve’ [of possibilities], it is the latter realm that becomes for him the phenomenologist’s quarry. Heidegger is using Husserl’s rubric that ‘the possible precedes the actual,’ which is to observe abstractly that ground comes before figure. (63)

Leaving aside the misuse of some of Heidegger’s terminology here,⁴ the notion that “the actual emerges as a figure from the ground” of possibilities (= from what McLuhan sometimes termed the ‘unconscious’), is exactly McLuhan’s basic contention. In this context it can well be said that “the possible precedes the actual” and that “ground comes before figure” (even though in our normal experience it is usually figures, effects and other such actualities that come before grounds, causes and possibilities).

To ‘precede’ and to ‘come before’ are temporal designations. But they are plainly questionable in this context (in the sense of provoking questions), since normally we have no experience of any such dealing between the possible and the actual. It was for just this reason that Heidegger gave his Hauptwerk the title of Being — and Time. Whatever the process may be between the possible and the actual and between figure and ground, it is their relationship in time that must above all be elucidated — and this not in some presupposed singular time, but in complicated times, plural, that are allowed to be just as questionable as what they would bind together (the possible and the actual, figure and ground) in some sense or senses of precedence and subsequence. 

Furthermore, as McLuhan pointed out in his 1978 conversation with Louis Forsdale, “the ground comes through the figure or the figure comes through the ground, it can be both ways“. Our usual experience of figure and ground, if we have one at all, is that figure comes first and ground later: lines and circles were familiar before geometry and physical materials before chemistry. Hence, what requires elucidation is not only (only!) the logic of the possible and the actual in their synchronicity (namely no physical material absent its elements and no message absent its medium), but just as much our peculiar diachronic experience of them (as a kind of laboratory) and, above all, the knotted relation of these com-plicated relations of the synchronic and diachronic.

The ambiguity of the treatment of phenomenology in LOM might be taken to reflect changes in McLuhan’s mind over time in his assessment of it. His declaration to Forsdale’s class in 1978 that he would rename LOM as The Phenomenology of Media would seem to indicate that he had overcome his ambiguity about phenomenology at the end of his career and had come to embrace it. Against this, however, it is necessary to consider the generally favorable assessment already made of Heidegger almost twenty years before. Here he is in The Gutenberg Galaxy:

Heidegger surf-boards along on the electronic wave as triumphantly as Descartes rode the mechanical wave.
The⁵ kind of ballet of mind choreographed by Gutenberg by means of the isolated visual sense, is about as philosophical as Kant’s assumption of Euclidean space as a priori. But the alphabet and kindred gimmicks have long served man as a subliminal source of philosophical and religious assumptions. Certainly Martin Heidegger would seem to be on better ground in using the totality of language itself⁶ as philosophical datum. (248)

And at the same time as The Gutenberg Galaxy, McLuhan concluded his 1961 ‘Humanities in the Electronic Age’ as follows:

The concept of history of the philosopher Heidegger recommends itself as a natural model for the humanities in the electric age. It is the idea of the poetic of history, of history as a kind of unified language, the inner key to the creation of which can be grasped by a deepening sense of the spiritual energy encompassed in the ceaselessly growing life of words. The ideal Marriage of Mercury and Philology, of spiritual values and perfected method, will be consummated, if ever, in the electronic age.

It would seem that the multifold relations of McLuhan to phenomenology await much future consideration. Especially, what did he have in mind proposing a title for what he hoped would be his crowning achievement that unmistakably suggested connection with Hegels Phänomenologie des Geistes (1807), Husserl’s Ideen zu einer reinen Phänomenologie und phänomenologischen Philosophie (1913) and Merleau-Ponty’s Phénoménologie de la perception (1935)? And especially to Heidegger’s notion of philosophy as phenomenological ontology?