I will only ever play on the computer. I have the apps on my phone in emergencies, like a power cut. The only other time I would use my cell phone if I were on the train or something, but I would only play play money to pass the time.
The computer has so many advantages; Screen size and multiple screens, ease of use, customise bet sizing, use of a HUD, multi tabling, multiple sites. A phone doesn't come close. The only advantage the phone has is that you can play poker on the toilet...