Hi @stellaparry
The phone is one of the Pantech C300 series.
You may not be able to get a SIM card for it in your location as the phone only operates on the 2G signalling band which has been or is being phased out in most places.
If 2G is still available in your location I don't know what size SIM card the phone uses, nano (8.8 x 12.3mm), micro (12 x 15m) or standard (15 x 25mm) but here's a page from the [https://www.manualslib.com/manual/259839/Pantech-C300.html?page=18&term=sim&selected=1#manual|user manual] that shows how to insert the SIM card. If you open the phone and check the size of the SIM card reader where the card slots into, this should give you an idea of the size of the card needed.