Graham Nye writes:

IIRC they were also called cell phones in the UK back when analogue
cellular systems were new, complete with diagrams of hexagonal cells
covering the countryside. Mention of cell or cellular has fallen out
of use in the UK to be replaced by "mobile".

Possibly because at that time, the term 'mobile phone' was often used
for a phone permanently fitted in a car or other vehicle. ISTR that if
you wanted to call one (from a landline) you had to go via the 'mobile
operator'.