the real question is will you be able to online check-in & get a boarding pass in advance OR will you need to get checked-in for China Eastern's flight once at LAX (and thus are subject to China Eastern's check-in cutoff time).
it won't take your more than 15 minutes to get from deplaning at T4/T5 from PHX (assuming mainline AA) to the LAX Bradley landside check-in (or Bradley's airside common self-service check-in machines on the walkway from T4 to Bradley).