How to transfer subscriptions between two Apple IDs?

I had to get a new Apple ID as well.

Why a new Apple ID?

Use the same Apple ID, then the subscriptions will automatically be transferred to your new iPhone.

Your Apple ID is the personal account you use with all Apple products and services. It includes the email address and password you use to sign in, as well as the contact, payment, and security details that you use with Apple.

You can’t merge multiple Apple ID accounts.

See the following Apple articles

Sign in with your Apple ID -> Sign in with your Apple ID - Apple Support

Manage and use your Apple ID -> Manage and use your Apple ID – Apple Support (UK)

I can explain the use case: I started a new job, the company policy requires using a corporate mobile device (no BYOD) they manage with MDM and require creating a corporate Apple ID with the company email address. It is ok to use the device for personal stuff, too. I have a few personal subscriptions I'd like to use on my corporate device.

Apparently, this is not possible. Either I buy these subscriptions again and lose money or I stick with two devices. Both inconvenient solutions.

It is not possible to transfer subscriptions. You must end the subscription on your old Apple ID, and resubscribe on your new Apple ID.

Best of luck!