Communication is a significant skill of humans. We have social skills how to communicate with anyone. Without Communication we can't even survive . So as per the question . Face to face Communication is very important than telephonic conversation.
Once you are talking face to face you get to know about the persons behaviour also but on mobile phones this is not possible.
You can clearly show your emotions towards the person you are talking . You can hug or as you know eyes can say everything.
You might be formal many times in telephonic conversation but you can be friendly during your face to face interaction.
Also face to face interaction will increase or boost up your Communication skills. The way to talk . The way to show your interpersonal communication skills.
Also when you are talking Face to face your confidence will also increases.
Hope you will be satisfied with my answer.
Thank you!!