Since the changes cause the departure/arrival times to change by more than 90 minutes, you are entitled to change your flights without a fee, within reason.

Look up the new schedules, as if you are booking your MAN-PHX round-trip from scratch.
Build and itinerary that works for you according to the new schedule, and call DL to update, and they should not charge a fee. Don't know the UK number, though.
It appears that switching the domestic legs should resolve the issues.

You should be able to move a day back or forward if that works better for you, but not more than that, unless the agent is really sympathetic.
You can also look at different routings, but destination must be PHX.