I am not able to see many contacts after iOS 17 update on iPhone

Contacts on iOS and iPadOS devices are synced to an email account and is not affected by iOS updates.

Contacts on iPhones and smartphones are not stored locally but are synchronized with email accounts. The primary storage is on the email server, with a local copy on the device for offline access. Syncing allows changes made on any device to be updated across all connected devices. You can sync contacts with various email providers, enabling access from multiple devices. This method ensures convenience and seamless management of contacts across platforms.

When you add and enable the Contacts feature on your iPhone, it provides you with the ability to sync your contacts with a specific email account. This email account can be from various providers such as Google, iCloud, AOL, Exchange, Outlook, Yahoo or any Other email client server that supports contact synchronization.

Please see the pic below for a better understanding...

If you are unable to find your contacts which were stored on iCloud, then try this --> Restore contacts, calendars, bookmarks, and more using ...

Check if the email account has been removed from the iOS mail app.

Add the email account that stores your contacts in the IOS mail app and enable Contacts.

What is your default Contacts account? If none, please add an email account and enable contacts.

See the pic below

Unlike some Android devices, contacts are neither stored locally on an iPhone nor in SIM. They are synced to an email account that you had Google, iCloud, AOL, Exchange, Outlook, Yahoo or any Other

If you have a corporate email account added through a profile on your device, please check with your organization's system administrator.

iOS updates aim to enhance user experience, boost security, and fix bugs rather than disrupt core features. Contacts issues after updates might stem from underlying, unmentioned factors. Updates won't typically alter personal data but may refine settings or features. Backup before major updates for safety. Review Apple's update details and backup advice for a smooth process.

Kindly consider checking your settings and addressing any device issues before attributing the issue to external factors. This could be a pure coincidence that the iOS update affected the iPhone Contacts.

Before initiating a standard iOS update, it's advisable to create a backup. Have you completed this step? If yes, proceed with the restoration from the backup.

See what each update does: About iOS 17 Updates, About iOS 16 Updates, About iOS 15 Updates, About iOS 14 Updates, About iOS 13 Updates, About iOS 12 Updates, and so on...