Processes in Microsoft 365 for setting up Office apps, redeeming product keys, and activating licenses.
Hi, Sean
Good day!
Thank you for posting to Microsoft Community. We are happy to assist you.
According to your description, the issue of your concern that your deleted contacts still syncing on your mobile devices.
First of all, please allow us to confirm you deleted contacts in which application, whether Outlook mobile, Outlook desktop client or via the website?
Please be kindly to have a check on your Outlook desktop client as following steps:
To delete a contact from one of your contacts folders:
- On the navigation bar, click People.

- Select the contact you want to delete and then click Delete on the Ribbon or right-click the contact and then click Delete.
If the issue persists, please be kindly to remove your accounts from your Outlook on your mobile device and re-add it back, then have a check to see if it can make any differences.
We're glad to assist you and looking forward to your new updates.
Sincerely,
Alex | Microsoft Community Moderator