EU national without UK phone number: Verification Process?

I am a German citizen and I want to rent a family house for four months in London. I found the house, the landlord will accept me, I will pay the complete rent for the four months upfront plus deposit. I do not have a UK phone number. Without the UK phone number I can not do the verification process. How could the landlord and I use the OpenRent contract process without a UK phone number?