I'm traveling in Canada and I don't want to use my company phone for private calls. I am also interested in minimizing costs but I am more concerned about relative anonymity. So I bought a SIM card locally and it works well. Will my employer still be able to see texts and log my phone calls? I want to avoid this.
I think M'vy gave the right answer in the comments, so I would like to expand on it in a full-sized answer.
Have a look at your threat model
People always say "I want to be safe". That's nice, but what do you want to be safe from? What is the possible attacker in your scenario, and what is their goal?
Are you afraid your employer might listen to your phone calls? Are you afraid the government is tracking who you are in contact with? Those two require radically different solutions.
Think about possible attack vectors
I will assume that your threat model is your employer tracking who you are in contact with. Different threat models require different solutions.
If you use the phone your employer provided you with, it's entirely plausible that your employer installed some spyware that listened to your calls and sent copies of those calls to them. It may not be legal to do so, but it's entirely possible.
If you use the SIM card provided by your employer, they are legally the partner of that contract. As such, they can an legally contact the phone company and ask for the log of conversation partners. This will list metadata of all incoming and outgoing calls, but not the contents of those calls. Depending on who your conversation partner is, this might reveal a lot about the contents already.
Think about possible solutions
The easiest solutions for both of these is to not use things provided by your employer. Mobile phones can be bought for less than 50 USD, some even as low as 30 USD. You already bought a pre-paid SIM card, so that's fine.
Keep in mind that this doesn't mean that you are 100% anonymous. Depending on the contents of your calls, you might be of interest to government organizations. In this case, you're on your own.