How can I add another one of my Apple ID to my iPhone?

In general no, not even more than one. There are a few places where you can use a different Apple ID, but even then in most you can only substitute, not use multiple entries:

1. In Mail if you want to use a different iCloud account. Settings -> mail -> accounts -> add account -> iCloud

2. Messages and Facetime. Sign into a different Apple ID for these services in Settings. Note this has to be the same ID for both. Go to Settings > Messages > Send & Receive, and make sure both your telephone number and Apple ID are input there and both show a checkmark. If you need more help, check out this link: Add or remove your phone number in Messages or FaceTime - Apple Support .

3. In the support article: If you subscribe to Apple One and use a different Apple ID for iCloud - Apple Support Apple alludes to using a different Apple ID for media, subscriptions, and purchases, but doesn't describe how to do this.

In iOS/iPadOS: Go to Settings > [your Apple ID] > Media & Purchases. Sign out of the current ID and sign in with a different one.

In Ventura: First, quit Settings. Then, in App Store, choose “Sign Out” in the Store menu, then click on the “sign in” button that appears in the main window. You can then sign into the other account. (from: Using different Apple ID for media & … - Apple Community )

4. Use a different Apple ID to share purchases with Family Sharing as outlined in Use a different Apple ID to share purchases with Family Sharing - Apple Support

A similar answer. An iPhone can only hold one ID at a time. Most of the features on a phone will be associated with that ID. In the few places where you can put a different ID, you again can only put one there. The exception is you can add multiple email accounts from anybody to the Mail app.

iPhones are not designed to be shared between multiple users. Since generally Apple intends each person to only have one account that means only one account per iPhone. If you get a new iPhone then you simply sign in on the new device with your old account.

Read this support article about Apple ID Frequently Asked Questions --> https://appleid.apple.com/faq

"How many Apple IDs do I need?

Just one. Use the same Apple ID everywhere you sign in to ensure that all your Apple services and devices work together seamlessly and you can access your personal content from all your devices."