That is really scary, more so when you think it was not illegal to use a mobile whilst driving.
The report says the man has sleep apnoea; from the picture of him, he certainly looks like a candidate for sleep apnoea which is very dangerous. However if that was a known condition before the accident (I can't remember if that was made clear or not), why was he still driving a lorry?
He was also driving at a far higher speed than allowed.
So, speeding and driving whilst looking at a text message. Extremely careless driving. Setting aside the sleep apnoea business, that is pretty serious.
I don't know what sentence he should service, am happy to leave it to the judge. Bearing in mind there was no intent to kill or maim, as a layman I would hazard a guess - three to five years, probably nearer five.