One way ORD-SFO-PHX, $111, available 5/23, 5/30
One way PHX-SFO-ORD, $111, available 5/16, 5/22, 5/29, 5/30, 6/5
You can also route through LAX for some days for less miles
RT same day return seems to be only available on 5/30 at ITA, with one leg by US, but cannot price it out on united.com:
United Chicago (ORD) to San Francisco (SFO) - Wed, May 30
United 971 Dep: 6:00AM Arr: 8:59AM 4h 59m Boeing 757 Economy (G)
United San Francisco (SFO) to Phoenix (PHX) - Wed, May 30
United 568 Dep: 10:21AM Arr: 12:25PM 2h 4m Airbus A319 Economy (G)
United Phoenix (PHX) to San Francisco (SFO) - Wed, May 30
United 3026 Dep: 1:40PM Arr: 3:39PM 1h 59m Airbus A320 Economy (G)
OPERATED BY US AIRWAYS Layover in SFO 2h 22m
United San Francisco (SFO) to Chicago (ORD) - Wed, May 30
United 818 Dep: 6:01PM Arr: 11:59PM 3h 58m Boeing 757 Economy (G)
Cost per passenger (including taxes & fees) $221.20
Total cost for 1 passenger $221.20