Is there a way to turn off the unlock pin?
Yes, you can disable this behavior either by unchecking “Enforce Device Locking” from the Clients > Device Configuration section of the Lync Control Panel, or by using the “Set-CsUCPhoneConfiguration -EnforcePhoneLock $FALSE”.
Also you can either disable this on the default global policy, or create a new Site-level Device Configuration policy and remove the phone lock option there instead