I don't think so; indeed, having someone "in the office" is a real asset- being able to do it 'on the cheap' is priceless.
You're in the field. You can't be hanging from a ladder and fielding calls at the same time. You also need to focus on things other than billing, payment, scheduling, etc.
I suspect more businesses fail from poor office practices, than from trade practices.
Apart from the obvious...being there, to answer the phone with "Joe's Electric- how can we help?"....your phone person needs to know a little about what you do, and who you deal with. They need to be "in the loop" for upcoming jobs, parts orders, and such.
One practice I would sugest is an hourly "call-in" by you for handling routine business. This will be when you return calls, receive messages, and such. Your customers should understand to call the office under any but the most exceptional circumstances.
In other words, your cell phne ought to ring only if the call is very, very time-critical. Most of these calls ought to be from your office- part of their job is to decide if the call can wait until your next call-in.
It might be tempting to use the office person as a permit filer, parts runner, etc....but that would be a mistake. When someone calls, they need to have the phone answered. Your office ought to realise that you will have to look at a job before you can price it- or even decide to do it!
His will not, strictly speaking, be a sales job. Not yet. As he get a handle on your abilities, and interests, he might 'branch out' into seeking customers (calling preoperty managers, getting you on bid lists, etc), that won't happen for a while.