How can I find how many Apple IDs I have with the same phone number??

Have a look at these steps:

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Because your Apple ID is used across all your devices and services, it's important to keep your account information up to date. Simply sign in to appleid.apple.com at any time to manage your account:

• Update trusted phone numbers and devices that you're currently signed in to with your Apple ID.
• Change your password to help maintain the security of your account.
• Update your Apple ID email address to make sure it's an address that you use frequently.
• Add additional email addresses to help people find and communicate with you on Apple services like FaceTime1, iMessage, and Find My. You can also use these email addresses to sign in to your Apple ID.
• Update the birth date associated with your Apple ID.
• Change your Apple ID country or region.

You can also learn how to manage your payment information on your iPhone, iPad, or Mac.

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copied from: Manage and use your Apple ID - Apple Support

You would have to check each account and see the phone numbers it uses.

To see, add, or change your trusted phone numbers use one of these methods:

● On your iPhone, iPad, or iPod touch: Go to Settings > your name > Password & Security. Next to Trusted Phone Number, tap Edit.

● On a Mac computer choose Apple menu  > System Settings (or System Preferences), then click your name (or Apple ID). Click Password & Security, then add or remove a trusted phone number.

● Using a web browser:

1) Go to https://appleid.apple.com and sign in.

2) Follow security options until you find one letting you change trusted numbers,

3) Click "+" to add a new number (you may be required to verify this number).

4) If you wish to remove an old number, click "-" next to the number.