Debenhams is a good mid-market retailer, and Marks and Spencer is a similar operation. Primark also has some well priced bedding and clothing options - it’s very much at the fast fashion end of the market, but if he’s only going to be there for a year it doesn’t need to be top quality anyway. Unfortunately there’s no IKEA within easy distance of Oxford, but they do deliver and it can be a useful supplier of all things household.
There’s some info on which the best student accounts are http://www.moneysavingexpert.com/students/Student-bank-account although some banks can be a bit funny about international students. If you can, try and get it set up in advance - I’ve seen long queues form outside of banks very near to universities as international students all try to set up an account simultaneously.
For his phone (or ‘mobile’, if we want to use British English!) it’s probably easiest to just get his phone unlocked so that he will be able to use it on any network, and then get a GiffGaff sim card - it’s a very low cost provider that just has rolling 30 day contracts, so he’s not tied in https://www.giffgaff.com/