Question: how to transfer all contacts from one android phone to another?
Answer: Android gives you a few options for transferring your contacts to a new device. ... 
Tap your Google account.
Tap “Account Sync.”
Ensure that the “Contacts” toggle is enabled. ... 
That's it! ... 
Tap “Settings” on the menu.
Tap the “Export” option on the Settings screen.
Tap “Allow” on the permission prompt.