Risk of undue influence: the lawyer doesn't know the circumstances of the caller-- is there a gun to his head? Also, lawyer should maybe return the ripped-up pieces to the client, just for the sake of closure.
Law in action: a decisionmaker might revive the will if it seems closer to the testator's intentions than intestacy. That's the sort of factor that might make telecommunication seem like a bad idea. Of course, if the will is gone, then it's gone, and maybe nobody knows what was in it-- it could be revoked just de facto, regardless of whether the revocation was properly done.
Maybe-leaning-towards-yes is a credible answer. Under § 853.11(1m), partial revocation is OK (not all states allow this, by the way, nor do all allow revocation by physical act). And there's complex law about canceling, but these lines go right through the words (that's what is required).
But what is the difference between tearing up a page and tearing out a page?
And does someone, in a fit of rage, have capacity to revoke a will?
So those are possible issues, and they might influence the outcome, depending on where the decisionmaker wants to go.
Anyway, if the will is revoked, the whole estate goes to the charity. This means the charity is kind of a big decisionmaker here-- maybe they don't want to be the source of acrimony. Of course, the size of the estate might also be a consideration. In general, charities don't like to get into spats with donors and their families. Every rule has an exception, though, so you never really know.
Part A: There's property, a settlor, some terms, intent, and a trustee, so the short answer is yes. § 701.01 : all the elements are there. Trusts do get created orally, and can "arise out of a manifestation of intent. § 701.01(7). And we've got that, if the decisionmaker is willing to say so. Not all decisionmakers might read the Jimenez facts the same way. Note that the court could well have entertained dispute about the terms, but they just sort of accept that it's for education.
Part B: We assume the settlor is still alive. In WI, we assume it's irrevocable unless explicitly said otherwise. The default is irrevocable here, but that's in caselaw, not in the statute. So when you make a trust, say explicitly what you want-- maybe even in the title of the trust. You don't want ambiguity.
Part C: Taxing authorities might care; college financial aid people would want to know if she had this asset or not; creditors might like to know. We don't need to know in detail what their interests are, or what the implications are, but we do need to know that it matters what assets people have.
Part D: Statue of frogs- no oral transfers of land. You might get a constructive trust as a result (if unjust enrichment would result otherwise).