Changes on contacts are not replicated to a mobile device.

This is a result of GMS user that has never access his account via WebPIM interface but since beginning used only his mobile device. You can create a GMS account via auto-discovery feature of GMS also login in via mobile device but this method leaves several configuration options of GMS account untouched. It is advisable to create GMS account rather via WebPIM interface and finish configuration or do it at least any time later to see / change settings.

In this particular case, after login into GMS account via WebPIM interface, Settings tab and "Pick Contacts to Sync" configuration option, it was found that there was only the "Sync only contacts in these categories" option selected and none of address books listed bellow was activated.

Please note, that if you click on Contacts tab in WebPIM, you will see all contacts listed from Frequent Contacts address book although this option was not selected. The contacts from Frequent Contacts are always synced into WebPIM interface, though, as far as you do not activate it from Pick Contacts to Sync, these are not going to be synced on a mobile device.