Julian Saunders, who writes the Sandwell Skidder blog, was outside Oldbury Council House filming elected members ahead of a full council meeting on Tuesday.
In the video, Mr Saunders was filmed calling out to councillors as they walked into the building, stating: “Councillors, back to the future? More corruption? More cronyism? More incompetence?”
Councillor Steve Melia, a Labour member for Great Barr, then pointed a finger at Mr Saunders, saying: “Have I given you permission to film me? Have I given you permission to film?”
Councillor Melia continued to ask the question before knocking the phone out of 63-year-old Mr Saunders' hand.
West Midlands Police is investigating the alleged assault but so far no arrests have been made.
Meanwhile the video has been viewed more than 90,000 times on Twitter and has led to calls for Councillor Melia to be suspended.
Councillor Melia has declined to comment on the incident.
Mr Saunders said: “I have been interviewing councillors before meetings in Oldbury over the last seven years. During that time I have been subjected to vile abuse from Labour councillors, but this is a first.
“Councillor Melia has been filmed many times, and usually has plenty to say for himself, and so this was completely out of the blue.
“Sandwell police contacted me very quickly after this incident and their investigations are ongoing.
“I hope the Labour Party will suspend the councillor pending their own investigation into this appalling behaviour.
“I shall also be making a formal standards complaint to the council although I have no expectation of satisfaction via that process as currently operated.”
Stephen Peugh, 57, from Bristnall, was outside the council chambers as part of a protest with the Brandhall Green Space Action Group.
He said: “I was standing here in the rain and then I saw [Julian Saunders] filming the councillors going into the chambers. I saw Councillor Steve Melia walk straight up to him and knocked his phone straight out of his hands.
“It’s as simple as that. He appeared quite angry.”
Bob Dunn, 73, a retired police inspector for West Midlands Police, was outside Oldbury Council House when he picked up Mr Saunders’ phone off the ground.
He said: “He moved across the car park towards [Julian Saunders]. He has his phone up towards [Councillor Steve Melia], filming his face. He knocked it straight out of his hands.
“I think it’s disgraceful. A member of the public office, to act like that. It is not behaviour I would consider someone of a councillor status should do. Or any politician for that matter, to retaliate like that.”
Another eyewitness, who wished not to be named, said: “I saw the contact happen, when the phone was jostled around.
“I thought what happened last night was out of proportion. I thought it wasn’t called for.”
A spokesman for Sandwell Council said it was aware of the matter and would be discussing it with Councillor Melia.
“The council will consider any appropriate action in accordance with its Ethical Framework that governs elected member conduct," they added.
“The council expects all members to abide by the standards set out in the members’ code of conduct. The council supports freedom of expression and speech and the rights of the press to attend council meeting that are held in public.”
A spokesperson for West Midlands Police said: “We’re investigating an assault on Freeth Street in Oldbury, Sandwell around 4pm.
“It is understood a man in his 60s was assaulted by a man in his 70s following a verbal altercation.
“There were no reported injuries and no property was damaged. We are aware of a video circulating on social media and we ask people not to speculate on the circumstances at this time, as it hinders our investigation.”
The council confirmed the incident took place on council property.
The Labour Party has been approached for comment.