Did the disciple Philip witness Jesus turning water into wine? To my knowledge the verse doesn't explicitly state which disciples were with Jesus but is it known whether Philip was traveling with Him at that point?
According to the text in John 2, the only ones who actually witnessed the water turn to wine were the servants.
The Disciples were invited to go with Jesus to attend the wedding per verse 2. However, the only people listed in the back room who actually witnessed the water turn to wine, away from the view of the guests, was Jesus and the servants according to verse 6. This is emphasized in verse 9 where the text says the servants knew and it does not say that the disciples (at that time) knew.
The vessels: the vessels were vessels or stone sinks used for purification. They were not vessels used for drinking water. They were basically kitchen sinks used for washing hands, washing pots and pans after a meal "vessels for purification." I would think, since it's mentioned, it is important and meaningful.
This narrative illuminates the reason why Mary told the servants to do whatever Jesus tells them. They were told not only to fill the kitchen sinks with water, but also told to draw the water from a place you would never drink from, let alone give to wedding guests to drink. However, when the servants, who were obedient, drew the water and served it to the guests, the master of the feast is the one who is the first to let the reader know that the dishwater was turned to wine.
That it was turned from water (water that went into the kitchen sink) into wine was realized by the servants after they drew it and served it per verse 9. I think about the relatively tiny fraction of those privileged enough to actually witness the miracle; specifically, we know it was the servants and of course the Lord because they are the only ones mentioned who filled the vessels then drew the water and served it to the guests.
The Disciples are mentioned nowhere in the entire incident except that they were invited, they attended, and because they too found out about the miracle of water turning to wine (verse 11) they believed in Him.
For me, the blessing is in the details. Vessels used to clean the outside were used to change the cleansing material (water) in a supernatural way to a material used to cleanse the inside (wine); a picture of the supernatural power of the Holy Spirit, three days after the baptism of Jesus; death, burial, resurrection to new life.
Since it's not specifically stated in the passage yet may be gleaned from other passages in John and in the synoptics, exactly which disciples were invited along with Jesus, (I think all of them were) is not important.
While the scriptures don't name the disciples present at the wedding at Cana we do know from scripture that Philip became a disciple of Jesus on the second day after his baptism. John 1:43 reads, "The next day Jesus decided to go to Galilee. He found Philip and said to him, “Follow me.”" As one of his chosen disciples it can only be assumed that when John wrote in relation to the wedding, "Jesus also was invited to the wedding with his disciples." (John 2:2) that all of his hand picked disciples, including Philip, were present to witness the first miracle Christ performed. John concluded with this by writing, "This, the first of his signs, Jesus did at Cana in Galilee, and manifested his glory. And his disciples believed in him." (John 2:11)