Done that. I just get the initial 15GB that I got from enabling the same option on my tablet. I can understand if you just get it only once no matter how many devices you buy, but it's not advertised like that and was sold as giving me 30GB with the phone.
Anyway, I've discovered there's a current offer for a year of Office 365 inc 1TB of OneDrive, but there's nothing with the phone about it. You have to install the Office 365 Gift app. I seem to qualify although the activation site is broken (continue button does nothing).
Though I'd still like the 30GB which I believe would be for life. Office 365 is okay but I already have it through my freelance business, though that doesn't give me the 1TB for personal use. Not fussed about paying ?8 a year after the free year for the 1TB. I really just need about 200mb to cover documents and bits plus my photos (big raw files included), which I can pay less for, or manage to get enough freebies to get that much. I'm on 140MB through freebies though 100 of that is another 1 year offer.