what happen if i erase all content and settings if my find my phone on it will be locked by activation lock

No. If you are the owner of the device and the Apple ID that is on the device then your device is safe.

Activation lock is only for those who do not have access to your device Passcode and Apple ID credentials.

Don'ts

If the device is removed from an account after it is erased, Activation Lock will be turned off. This allows another person to turn on and use the device.

An example of my iPhone 5 is given in the GIF below. There is no "Undo" after you remove it from your account.