Hi everyone...
I hope everyone is healthy (physically & financially) and surviving the current situation.

A general update to my situation.
With the new city ordinances and other health related requirements that our local governmental officials have imposed, we have not only furloughed several employees, but have had to alter our daily operations. Thankfully, with my position, I've not received any notification (yet)...and remain to be sure our infrastructure for remote desktop and other services are functioning. That said, our office phones have been silenced since those not furloughed have been working from home....which is good & bad. Good in that I don't hear the complaints when the problem arises (I'm joking) and bad in that I have no way to test the problem in a persistent way. But I do thank EVERYONE for their input and suggestions!

@EV60797...
Thanks for your suggestion. Yes, originally I did just exchange the handset...but also exchanged the telephone sets also on a couple of employees desks. We have several NOS (New Old Stock) stashed away when our company downsized in 2014. So far (before the situation we're current in) the problem has persisted....so I don't believe it is in our handsets and telephone sets. Not definitively discounting that it could still be, but I'm leaning toward it's not.

Measuring voltages and other testing on the phone system is a bit beyond my scope. I've had very limited experience in that (other than the basics). Might be time I invested in a few devices (they might have them discounted in our current economic situation). I'm just not sure that a novice (myself) should be handling things that might require a more experienced (and efficient) technician....but I'll do a little reading (and YouTube?) and see what I can do. You've given me the specifications that each line should be, so I'll report back when I have results. I appreciate your help.

However, you are correct that it was designed in a time before all the new technical innovations that are currently offered. I also checked and the devices (Spectrum EMTAs) are Arris TM804G (we have 2 of them)...although we have had them exchanged out several times since we began with then several years ago. I've often wondered about their (Arris) reliability, but only from a curiosity standpoint (because they were so readily changed out when a Spectrum technician came to address previous situations).

@Carl Navarro
That was my question to Spectrum (call logs). Although they do have call logs for billing purposes, they don't match up for technical diagnosis purposes (at least according to the Spectrum representative I spoke with). They wanted me (and our employees) to notate when they had problems. Date, time, phone number, land line or cellular number, incoming or outgoing...etc. I created a spreadsheet for the employees to note (before the ordinance closures began)....some did, some didn't (which is par for the course where I work). I did get several good data points....and submitted them to Spectrum (along with the matching times on the billing statement). Unfortunately I've not heard back from them (as of this writing).

Thank you both for your valued input.
I appreciate the time you spent replying to my question...and will do my best to test our equipment (to be sure it's not the problem).....but my gut feeling is that it is something upstream (ie, Spectrum related) from our offices. I'll report back to the forum....maybe this will be beneficial to someone with similar problems in the future.

Stay safe, stay connected....