"I'm glad to hear you!" really isn't correct unless you are saying you glad that you can physically hear someone, such as if you had phone trouble, "We had a bad connection, but now it is very clear. I'm very happy to be able to hear you now." To express you are happy to speak with someone, then use, "I'm glad to hear from you!" or perhaps, "It's great hearing from you."

I assume the saying you meant was 'I'm glad to hear from you'. In that case, you could also say: 'I'm happy to hear from you', 'Great to hear from you again' or, 'It's so good to hear from you again'. If you want something formal, you could use: 'Thank you for getting back to me' or, 'I appreciate you taking the time to contact me'.