W1zardK1ng if you are concerned about security on your work phone, probably an unlocked and outdated (security/firmware updates) OS will not do you any good. A work profile on your GOS phone is therefore your safest bet. It seems like you want to use apps on your work phone that require it to be connected to the internet (Teams, Outlook), and that to me looks like a big risk. Connecting your outdated, less secure hard- and software to the internet should be by far less secure than using a work profile on GOS with all the security patches and extras (check out the exploit protection feature list to see what I mean).
If you want a secondary device, I recommend you reconsider buying another Pixel device. I bought a second Pixel for work because of some things profiles can't do (like only register a SIM card with phone number on the work device, keeping the private phone somewhat "clean" with a silent.link data eSIM). Pixel 6a devices are very cheap nowadays, especially considering the 4 years peace of mind they will still give you. Maybe you'll find them even cheaper used or get your employer to pay for one. Sell your old phone or trade it in if the seller supports it, or use it for something less critical (like an offline only media player or a nice paperweight :)). That's all just my two cents, consult your threat model and find your best answer, in the end only you can decide what's best for you. I hope this post is able to help you evaluating the (lack of) security of your old phone better.
Edit: If your phone can replace your work laptop, maybe you want to get a Pixel Tablet when it's on sale and use that instead of your laptop or old phone. If you can sell your laptop and old phone to further lower the tablet price, you'd have the safest work device and safest phone. I'm very close to just doing that, and it works really well once you got used to the different user experience.