iMac to iPhone

Hi VAivars1,

Thanks for using Apple Support Communities. Since calendars on your iPhone and iMac are associated with either iCloud or a third-party email account, it may be best to first make sure that you have all of the same calendar accounts on both devices.

You can find current accounts on your iMac by going to the Calendar app, then Calendar > Accounts. If you need to add an account, you can do that using this guidance from Add or delete calendar accounts on Mac - Apple Support.

"Add a calendar account

1. In the Calendar app on your Mac, choose Calendar > Add Account.
2. Do one of the following:

• Select your calendar account provider, click Continue, then follow the onscreen instructions.
• If your calendar account provider isn’t listed, ask your provider for the information you need to enter. 
• Choose Other CalDAV Account, click the Account Type pop-up menu, then choose an option based on the information you need to enter.
  • Automatic: Choose this option if you just need to enter your email address and password.
  • Manual: Choose this option if you need to enter your user name, password, and the server address.
  • Advanced: Choose this option if you need to enter your user name, password, server address, server path and port number. You can also select checkboxes if you need to use SSL or Kerberos v5 authentication."

On your iPhone, you can find current accounts from Settings > Mail > Accounts. If you see that any are missing, you can add those using the following steps from Set up mail, contacts, and calendar accounts on iPhone - Apple Support.

"Set up a mail account

1. Go to Settings > Mail > Accounts > Add Account.
2. Do one of the following:

• Tap a service—for example, iCloud or Microsoft Exchange—then enter your account information.
• Tap Other, tap Add Mail Account, then enter your account information."

Kind regards.