Hi,

What cabin are you in?

If in F or CW you should be clear of customs fairly quickly ( I have done it in 20-25mins being in CW)- however that is with no other a/c in front of us.

PHX is very good for entering ( on the other hand if in WT it might take slightly longer as there are fewer CBP staff than other airports ( but less pax also)

From exiting customs it is a bit of a hike ( then an elevator to the main public area of T4 then another elevator to check in)

I do not know minimum check in times for US Airways but I would leave at least 2hours ( also to allow for any delays on the BA flight) .I assume if you miss the US airways flight they could put you on the next flight for little/no charge. If the charge is high you may want to build in more leeway.

Regards

TBS
PS on the return, US airways may be able to tag your bags to PHX then LHR so you do not have to collect them at PHX ( and with PYOBP you could head straight from the US airways gate to Gate B22 and up the stairs to the BA lounge ( the BA flight has left from B25 in my experience)

Enjoy LAS!