transfer the phone contracts to another person

So you mean a mobile contract? 

You can do it in “Mein O2” App.

Go to: Einstellungen → Vertrag verwalten → Vertragsinhaber wechseln

Hello ​@begumtepetas,

welcome to our o2 Community 🙂

The way 5G_Tester describes you can transfer your contracts to other persons, for them this costs a one-time fee of 34,99 €.

Discounts like Kombi-Vorteil and for hardware are not transferred.

Best Regards,

Gerrit