The First Minister defended the scheme, which has cost more than £4 million, after being accused of dishing out "freebies for criminals".
Conservative MSP Russell Findlay said the devices had been misused thousands of times, including to order firebombings, deal drugs and threaten victims.
He asked Ms Sturgeon about the issue at First Minister's Questions in Holyrood.
Ms Sturgeon said: "At the start of the pandemic, we took the decision to provide mobile phones to those in custody to maintain vital family communication, including, and perhaps especially, with children during what was an incredibly challenging period and when normal visiting, of course, was impossible.
"Between then and April, the amount spent to date is £4.12 million."
Mr Findlay accused the Scottish Government of slashing budgets for the police, courts and prisons, adding: "Money is tight, we get that.
"So how on earth can mobiles for prisoners at a cost of £4 million and rising be a priority? Taxpayers' money should be spent on frontline services, not freebies for criminals."
He said the phones had been used "to order firebombings, drug dealing and to threaten crime victims".
Mr Findlay, a former investigative journalist who reported on organised crime groups, added: "Prison officers tell me these SNP-issued phones are putting them in danger by fuelling violence between inmates."
He called on the First Minister to "bin this costly and dangerous policy".
Ms Sturgeon said prison should be about rehabilitation as well as punishment, adding: "It is important that we don't lose focus on that."
She said the scheme is about "ensuring connections between prisoners and families, including children, which is important to rehabilitation, which is important to reducing offending and reoffending”.
She added: "So we will continue to consider all of these issues carefully, but we will consider them in the context of a justice system that yes, punishes criminals – that is extremely important – but one that also seeks to rehabilitate those who commit crimes and reduce reoffending, because that's in the overall interest of communities across the country."