Stop and fish.
Has anyone considered doctoring their phone such that it breaks when Constable nobhead tries to open it?
You broke my phone and I'd like a new one, please. Come on, come on, pay up, I haven't got all day.
Anyway police don't have carte-blanche to do what the fuck they like. Believe it or not they operate under a code of practice, which code of practice gives examples of what counts as reasonable suspicion. "Having a phone" is not one such example.
A summary of which legalistic guff is (cf. http://www.yourrights.org.uk/yourrights/the-rights-of-suspects/stop-and-search/reasonable-grounds-for-suspicion.html):
"There must be some basis for the officer’s belief, related to you personally, which can be considered and evaluated by an objective third person. Mere suspicion based on hunch or instinct might justify observation but cannot justify a search."
A hunch such as "Well lots of people around here have stolen phones" isn't good enough; they much have a bloody good idea that /you/ have a stolen phone.
No suspicion, no search. No likee? Take it up with my solicitor: here's his number. Good-day, cunstable.