I think phone has became common usage enough to allow the dropping of the prefix apostrophe.
"Got a new mobile phone.". Even this becomes "Got a new mobile." with people assuming you mean a portable phone and not a spinning ornament attached to the ceiling.
Thinking about this though, my previous rant about "<Townname> Auto's" garage, they may be using this rule for the word Automobiles, so I will allow them away with it.
Bit like fridge, you don't say 'fridge' (for refridgerator).
I hate it though, when people say "MP3" for "MP3 player".
Or it used to be "Video" could mean the tape or the player. "He's got a new video".
Radio could mean the receiver or the transmission method, but as we rarely talk about radio waves it is somewhat acceptable.