Authentic means genuine and original, as opposed to being a fake or reproduction.
To be authentic is to be real, valid, bona fide, true, reliable, and dependable as opposed to fake or counterfeit. Jesus said:
I am the true vine, and my Father is the husbandman.
Every branch in me that beareth not fruit he taketh away: and every branch that beareth fruit, he purgeth it, that it may bring forth more fruit.
Now ye are clean through the word which I have spoken unto you
Jesus let us know through His teachings and demonstrated by outward display of works that He was the real not a phony or a want to be. When you are authentic your life will bear fruit of the trueness of your words.
John 14:11 (amp)
Believe Me that I am in the Father and the Father in Me; or else believe Me for the sake of the [very] works themselves. [If you cannot trust Me, at least let these works that I do in My Father's name convince you.]
Jesus was indeed who He said He was regardless if anybody believed Him or not. The proof of who He was was not based on the opinions of others but rather the life He lived. His life consistently mirrored the scriptures that prophesied of Him and the union He had with the Father. If God is in you then everything you do and say should be proof that He lives there. The book of Revelations declares that there would be those who had a name that they lived but yet were dead. (Revelations 3:1)
To be phony is to give a false impression, to make something appear to be genuine when it is not. It also can be putting on a false show of something such as sincerity or expertise.
A phony can only be detected when you know the real and genuine. Refusing to become familiar with the true can make you vulnerable to the fake. Take time to cultivate in your life the knowledge and ways of the True Vine and you will never be deceived by the counterfeit vine.