Honestly, we don't need GPS data to prove a victim was where she said she was. What if she had mobile data turned off when it happened? Like anyone on a low income would? Or if she'd run out of phone credit?
All the stuff in a mobile phone, it could help to secure a conviction, but claiming it's necessary or needed is a fallacy because that implies that, before the amazing magical smartphones became mass consumer goods, no rapes were ever prosecuted.
They were. Better than they are now. Presumably because we had more funding for the police and therefore more forensic psychologists to talk to suspects and victims, but I'm going out on a limb there.
The fact rape prosecutions are at an all-time low goes to show that the police are getting far too bogged down in unnecessary crap like whether a woman has a Tinder account or ever Googled "what the fuck even is a rape fantasy" or whether she's got erotic romance in her Kindle account, and not enough time actually investigating crime.
It's as stupid as the fact that poor 17-year-old's pair of knickers were used to get a rapist acquitted in County Cork a couple of years ago.
A phone is a valuable item, some of them cost a lot of money, and they devalue quite quickly, so the police keeping someone's phone means the victim has to get another phone for day-to-day use in the interim, losing money as their proper phone depreciates in value, possibly paying a phone plan for their proper phone, and having had to shell out on another phone especially if they need it for work.
Confiscating someone's phone when they report a rape smacks of a paternalistic schooldays attitude where all rape victims, regardless of age, are incorrigible children.
On a side note, this all seems like a reason to keep an old phone around to hand in instead, and to change phone numbers/providers once every couple of years like we all used to in the Nokia 3210 days.
You can bet that's what the rapists will be doing when they plan these sort of crimes. Which basically invalidates the use of any given phone as "evidence" for anything at all.