He was released from custody in the Florida city after posting his bond of $12,500 (£9,450).
He was charged with strong-arm robbery and criminal mischief.
McGregor's attorney, Samuel J Rabin Jr, said: "Last evening Conor McGregor was involved in a minor altercation involving a cellphone that resulted in a call to law enforcement.
"Mr McGregor appreciates the response of law enforcement and pledges his full cooperation."
A police report shared by Miami Police on Twitter said: "The victim and the defendant were exiting the Fontainebleau Hotel and the victim approached the defendant with his cell phone.
"The defendant slapped the victim's phone out of his hand, causing it to fall to the floor.
"The defendant the stomped on the victim's phone several times, damaging it, the defendant then picked up the victim's phone and walked away with it, depriving him of it.
"Victim stated the phone was valued at $1,000.
"The defendant was located and arrested."
Miami Beach police said they would not be releasing more details.
According to the Miami Herald, the 30-year-old has been in Florida for a couple of weeks on holiday as he prepares for his comeback.
Recent photos shared on his Instagram stories show him appearing to fight an alligator, and going on a boat tour with his wife and son.
McGregor lost his last fight in October 2018, to Khabib Nurmagomedov, and also lost a boxing match to Floyd Mayweather.
He has recently launched a fashion line called August McGregor, which sells modern suits to millennials. He also launched his own whiskey last year, named after the Dublin neighbourhood where he grew up.