Long or short telephone conversations can help to keep your relationship with your partner. Added variations of this includes phone dates using applications like Facetime or Skype. You can experiment and find out which method works best. It is also good to develop shared things that will bring you closer despite the distance.
Walking out and admiring the moon or stars as you talk over the phone is one good example. You can also establish a routine of texting ‘good morning’ to start the day. You can experiment and see what ritual is appropriate for you.