If you are paying per hour, it doesn't matter whether he is self employed or on a payroll, it is reasonable to expect him too be working fairly consistently for those hours.
Its one thing if he's to be paid to complete a specific brief - when I had my garden done there were a list of things to be done, mainly landscaping stuff, so if they wanted to sit down and have a cup of tea and a chat (which they did several times a day) that was great, because they were managing their time, they knew when they wanted to hand over the job, get payment, and move onto the next job.
Someone on an hourly rate however, may be taking the piss, if they are stopping to text and do stuff on their phone every few minutes (if that is the frequency)
I have cleaners who are paid for 3 man-hours (so they send 3 and are here for an hour). If they were on their phone a fair bit of that time, they wouldn't get the job done and I would be seriously miffed.
If I just paid them to clean my house from top to bottom, however, rather than "3 hours", then they could spend as much time texting as they like, if they want to be here for 8 hours that's their problem (though actually it would be mine a bit too, however, they don't so its not an issue).
If you are paying someone by the hour, I think its fair that you get 55 minutes work per hour (which works out as having a 15 minute break every 4 hours which is in line with what people would be entitled to if they had an office job). Anything less and they are unfortunately taking the piss a bit.