You may be disappointed with the lounges. They're a cut above most shared airport lounges but they're ultimately fairly bland, corporate lounges. Certainly no Clubhouse. And the ones in T5 are always busy even though the south one is HUGE.
Food is serve yourself buffet-style - the hot offering is "gloop" like curry, chilli & pasta (and jacket potatoes), but it's only available at lunchtime and dinnertime (or breakfast in the morning). In the middle of the day it's just sandwiches, salads & snacks. The caterers have changed in the past few months, sparking a very angry and vociferous backlash from the BA brethren over on Flyertalk.
The bar is also serve yourself - no cocktails alas!
Not tried the Elemis spa but there's certainly no hairdressing.
There's a quieter, smaller lounge in the T5B satellite, which is worth investigating if the PHX flight leaves from T5B or T5C. The trouble is they don't tend to announce the gate numbers until relatively close to boarding, so if you take a chance and catch the shuttle to T5B only to find the flight goes from the main terminal, you're a bit screwed as it's not easy to get back.
In the air - CW is a good product but, like UC, it has positives and negatives. The food & wine are widely thought to be better than VS. The seat itself is good - no need to get up to turn it into a flat bed - and the service is consistent & professional.
But I personally dislike the moveable opaque screen between you and the passenger next to you which has to be down for take-off and landing - meaning you're looking straight at them - and with a 2-4-2 config downstairs on the 747 the cabin does feel a bit like a dormitory. Try for upstairs if you can, but unless you have BA status you'll either have to pay £80 to request a seat or take your chance at OLCI at T-24, by which time upstairs may very easily be full. Plus if you're not in an aisle seat, you have to clamber over the passenger next to you to get out, if they're using their bed.
For me, UC wins overall but you may find you love CW!