On licento.com, open Your devices and choose «Sign out my other devices»: every device except the one you are using is signed out at once.
There is no way to sign out one device on its own from somewhere else. The button signs out all your other devices, phones included, in one go, and the device you press it on stays signed in. You then sign in again on the devices you still use.
Setting a new password does the same: whoever knew the old one is signed out everywhere. If you think someone else knows your password, set a new one with «Change password» in your account's settings.
On a phone you still have, you can sign out in Me. It needs a connection, and works once every answer has been sent.