log in from another phone…possible?please help

dear all,
my bf told me that his phone got damaged. that's why he can't be online on whatsapp. today, he sent me a whatsapp message…saying that he used his friend's phone. but it was his number and whatsapp. he then said his friend needed his phone back and that he had to go offline.

my question…is it possible to use whatsapp from another phone but with your phone number and whatsapp account?

I've some doubts…I appreciate your help…thank you