Tizen Developers

Use HelloAccessory sample from http://img-developer.samsung.com/contents/cmm/HelloAccessory_141006.zip

Make an android service and a matching gear app. (Integrated app.)

Use the Android API 

http://developer.android.com/reference/android/telephony/TelephonyManager.html#getLine1Number()

to get the phone number is HelloAccessoryProvider

Send it to HelloAccessoryConsumer on Gear.