Required Hardwear
Given that ABRSM require their exams to be taken on a laptop or desktop computer with a webcam and an internet connection, it is recommended that students log into online lessons using the same. It may be possible to use a large tablet for lessons, but not a mobile (cell) phone unless in exceptional circumstances. You would not be allowed to take the exam on a tablet or mobile phone.
Good quality sound is also desirable, so you may consider using head/earphones or an external speaker for lessons.
System requirements for ABRSM music theory exams can be found on the ABRSM website here.