If I have a device managed in GDMS and the device gets updated directly through its web interface, then the changes made directly on the phone do not show up in GDMS. Is there any chance we can get GDMS to reflect these changes under the device configuration?
No. This is how provisioning works.
You use the phone Web GUI only for specifics need or when not using GDMS/ZeroConfig/or any provisioning server.
Use GDMS to change settings. You can create users if needed to give them access.
Thank you for using GDMS platform! GDMS platform does not support reverse synchronization feature, which means the changes in your device will not be synchronized into GDMS platform. The is due to the security reason. If you want GDMS platform shows the changes, you can provision your device via GDMS platform, which means users can make the changes via GDMS platform. If you want more users to manage this device, you can give the authority to your sub-user account to manage the device.