Personally, I like all of those names. I'd say that they all have a 'girls grammar school comfortable middle class' vibe. No issue with that, obviously, but (as with all names) people will draw conclusions - that you may nor may not be comfortable with - from this.
Phoebe - Straightforward name that nearly everyone will be familiar with. It will be misspelled surprisingly often ("Pheobe"). You will not be able to avoid Phoebs as a shortening. The Friends connection is, I think, actually not a huge issue as the show over its lifespan has raised the visibility of the name to such an extent it has neutralised the name. When the show first aired, Phoebe was a definitely a slightly quirky, arty, unusual name, which befitted the character. These days, thanks to the enduring success of the show, the name has lost much of those connotations.You don't get expectant parents handwringing over the name Rachel, because it belongs to a character in Friends - the name is everywhere - and increasingly I'd say that's true of Phoebe, too.
Isolde - as the owner of a name with three mainstream pronunciations, I can attest to the fact that this will be a lifelong absolute pain in the arse for her. Spelling is a living nightmare. This one I think has more connotations of pretentiousness than the other two (I don't think it's pretentious, but I can definitely imagine some circumstances where some people might eye roll if you called her name across the playpark - especially if you are well-spoken).
Cordelia - Straightforward, easy to say and spell. Nicknames are not very nice (Cord, Cordy). Interestingly, I'd have said the literary connections aren't great (wet blanket in Shakespeare's King Lear; sadistic bully in Margaret Atwood's Cat's Eye; damaged and unfulfilled cipher in Brideshead Revised).