Since my own recollection was so faulty, it seems appropriate to print Phillips' own account here. And, since Wilson's biography is easier to find than Warnie's diaries, I've provided the less-accessable account here, taken from an editorial footnote provided by the editors to Warnie's diaries:
"Many of us who believe in what is known
as the Communion of Saints must have
experienced the sense of nearness, at some time,
of those we love after they have died. This has
happened to me several times. But the late C. S.
Lewis, whom I did not know very well and had
only seen in the flesh once but with whom I had
corresponded a fair amount, gave me an unusual
experience. A few days after his death, while I
was watching television, he appeared sitting in
a chair within a few feet of me, and spoke a few
words which were particularly relevant to difficult
circumstances through which I was passing. He
was ruddier in complexion than ever, grinning all
over his face and positively glowing with health.
The interesting thing to me was that I had not been
thinking about him at all. And I was neither alarmed
nor surprised. He was just there. A week later, when
I was in bed reading before going to sleep, he
appeared again, even more rosily radiant than before,
and repeated to me the same message, which was
very important to me at the time. I was a little puzzled
by this, and mentioned it to a certain saintly Bishop.
His reply was: 'My dear J, this sort of thing is
happening all the time.' The reason I mention this
personal experience is that although 'Jack' Lewis
was real in a certain sense it did not occur to me
to reach out and touch him. It is possible that
some of the appearances of the risen Christ were
of this nature, being known as versidical visions."
--BROTHERS AND FRIENDS, p. 288-289
Warnie's response was a mix of incredulity with despair. On the one hand, while not doubting Phillips' sincerity he wondered if he'd just "dreamt the whole thing", particularly since the vision spoke, wh. is not usually the case ("so far as I can recollect it is contrary to all stories of revenants, except the Witch of Endor; speaking ghosts are normally to be found only in literature or on the stage"). More bitter was the thought that his brother was able to manifest after death but not to him:
"why, oh why, if able to do so, should [he] never have come to me in the lonely study some evening with a word of comfort and good cheer? Is it that I am of such an earthly nature that to make contact with me is impossible for him? Perhaps he has so far outstripped me that I shall never see him again -- a horrible thought . . . Whatever the communication it seems to have been relevant and sensible, not the sort of slush by any means which is dealt out by mediums" (ibid.)
All in all, thin stuff to build a case for sainthood from, particularly since Phillips wdn't reveal the message. But in such matters it's often the case that those who want something to happen are far more dedicated and tenacious than those who don't want it, so I guess we'll see.
This sounds like the story told by Canon J. B. Philips, in which he says Lewis actually appeared and spoke to him (incident related in A. N. Wilson's biography of Lewis). Warren Lewis, C.S.'s brother, wrote in his diary (Brother's and Friends, Thursday 5th December 1969) of reading the story and being disturbed and depressed by it for several reasons.