Email Counseling and phone discussion are valid as counseling session as long as you have complied with all counseling requirements and the chain of command has approved this type of counseling due to geographical separation or other issue that prevents face to face counseling.
If we are talking about performance counseling for an evaluation report. It is mandatory to use the DA FORM 2166-8-1. The use of a DA FORM 4856 is optional and I highly recommend it but it is not a mandatory requirement.
However if there is geographical separation then phone calls can be used as an alternative. See extract below.