Stealing someone's phone is not justified under any circumstances, and certainly not in this case.
I have been on far too many dates. For the most part men have paid, for a coffee, or a couple of rounds of drinks. Sometimes I have offered to buy a round, usually that offer has been declined. I wouldn't be impressed if a date offered me a drink or two, then said 'your share of the bar bill is x' or whatever. If you buy a drink for someone that's it. If you only want to buy one drink, next time you say 'your round'.
£54 really isn't a huge sum (I know plenty of people who go for dinner on the first date which can cost maybe double that). It saddens me people think the woman is at fault here, simply for not offering to pay.
That sits ill with me; those of you who consider he was entitled to take her phone because she didn't pay her share, what would you say if instead of taking her phone, he'd forced a kiss on her, or groped/ assaulted her as 'payment'? If that would be unjustified (which it def would in my book) so is taking her phone.