Grant has now had his Facebook page removed after the Ministry of Justice stepped in and took "immediate action" to remove the content.
But the incident exposes how easily inmates can smuggle smartphones, SIM cards and other contraband into UK jails.
Taking a mobile phone into prison is a criminal offence, as is transmitting sounds or images from within a prison using a mobile phone.
But criminals sneak them in to continue their illegal activities.
Some inmates reportedly run drug-smuggling networks from prison. Jailed gangsters are also feared to have used secret mobiles to arrange for rivals to be murdered.
Since last November, when the UK Ministry of Justice put detection measures in place, over 13,000 mobile phones and 7000 SIM cards have been recovered from prisons.
Anyone caught with a mobile phone in jail faces an extra two years behind bars for the offence.
Ministers have also invested £2 million in hi-tech measures to block signals in prisons.
A Prison Service spokesman said: "This behaviour is completely unacceptable. We are clear that those who break the rules will be punished and can face extra time behind bars. We are taking decisive action to find and block mobile phones in prison."
Grant, from Stockwood, Bristol, pleaded guilty in May at Bristol Crown Court to committing grievous bodily harm with a machete.
The court heard how he attacked Neil Winterson in August 2016 while the pair were on their way to score drugs.
Grant hit him in the head in the street leaving him with blood coming out of his ear and left him with a partially severed right wrist.
Detective Constable Lee Booker said at the time: "He only stopped when two brave members of the public saw what was happening and intervened. I have no doubt the selfless actions of these two saved the victim's life."