My phone get stolen

I removed my stolen phone from my iCloud, however, erasing the phone has been pending for more than a day. Would whoever has it be able to access to anything on the phone if they were able to get in?

I had an airtag connected to it, but when I went to check on it on my laptop, the airtag wasn’t connected to it any longer, and when I tried to connect it on another account (my sister’s) it says that it’s registered on another account. The airtag has been kept in the same place from before my phone got stolen.