major issue with whatapp backup

Hi, I was hoping that someone would know how to help me, my issue is that i had an sony xperia and since Jan 2018 started to use whatsapp on it. Fantastic everything was good - I could talk to my family abroad - share recent pictures, just like that!!!!
I did do regular backups..... but not being super tech savvy I don't know where they have backed up to???????
So on Monday, I stupidly had my phone in my back pocket and when I went to the toilet - plop down the loo went my phone!!!!!!!! So the situation is... my phone won't switch on I think it has been completely drowned and is deader than dead.... I have still got the sim card and that does work in a different phone. (whoop whoop) however when I installed whatsapp it has not asked me to restore anything, so does anyone know how or even if , it is possible to restore my old conversations, videos and pictures. The sim card is the same number so please please if anyone knows how to do this, it would certainly put a massive smile on my face as I am very gutted over the loss of my phone, and all the photos etc on it
Many many thanks to anyone who can help xx