Merging Apple IDs or recovering Apple ID from a work account to a personal one

You can't merge Apple Accounts. Nor can you transfer purchased content from one to the other.

The correct way to have done this is to change the email address on the original Apple Account to the new work email address. However, now that you have already created a new Account with the new address, you can't do that.

When you sign out of your old Apple Account on you old phone, you should asked if you want to keep the data or delete it from the phone. If you keep it, then log in to the new Apple Account, you should have your data and pictures. If your contacts are associated with your old work email address, you may lose them.

You'll need to cancel your subscriptions under the old account and re-subscribe under the new one.

It doesn't matter if your old work email account will be deactivated before the new one is active. Your email address is just a username. Leave it as it is. Everything will continue to work just fine. When the new account is activated, change the the Apple Account from the old email address to the new one.

Change your Apple Account primary email address - Apple Support

Apple has never said why they don't allow accounts to be merged.