If we try to look logically at what you share then there are a couple of reasonable explanations for why they talk, but there are also some really big red flags…
Like it’s reasonable that coworkers commute. Depending on the job they are doing and location then even hour-long convo’s can be normal. One of my main coworkers is a female and works about 500 miles from where I am, so we might have anything from short calls to hours of Team-meetings (nearly) every day. We even share about family and I would consider her something between an acquaintance and friend. I guess about half the people I work with and interact on a daily basis are female, and I guess that if I or one of them were to quit we are all on good-enough terms that we would stop for a coffee if we ran into each other a year from now.
So… if hour-long convo’s are norm for the job and are a requirement to get the work done… fine.
Would these conversations be in-line with his job? Is he calling her work-phone or personal phone?
However… talking about relationships is out of order. It’s a very slippery slope. A delicate line. Like that colleague of mine? I know she has three kids. Know one is in college and doing well. Know her husbands name and job and have even talked to him at company-events (he’s an angler like me). Know they bought a truck this year. But that’s about it…
The Red Flags…
The number hidden behind a man’s name.
Why? Is there any logical reason for this? I can think of excuses – but they revolve around your husband knowing you would have an issue and therefore hiding it. Red Flag.
Talking about her relationship(s).
This raises some issues… People should know to keep a certain distance from their issues and work. Discern between associates, acquaintances and friends. If he is in any way her superior at work (like her boss) that distance needs to be heavily enforced. That he seems to break that… a big Red Flag.
Disproportionate time talking to her…
Look – I’m all for work being fun. But work is work. It’s bring-home-the-bacon time. I might spend hours talking to my female colleagues but that will be billable hours because we are talking about work, not if her husband is a douchebag or what happened in last episode of The Crown.
So what to do?
For one his promise not to talk to her won’t work…
For one, he probably does need to talk to her for work. For two, if he didn’t recognize this as a threat to the marriage (despite recognizing this as something he needed to hide) then he will relapse. Only this time be more careful.
We have more-or-less standard suggestions for budding emotional affairs:
Go get a copy of the book Not Just Friends by Dr. Shirley Glass. Tell your husband that the two of you should read it. Preferably together. You can even get an audio version and listen to it together.
The key here is that you are 100% certain it’s read. Like if you get an audio copy the two of you find some quiet-time together in the den, sit with your coffee or tea and LISTEN. Stop and discuss each chapter. Do the exercises.
What this will hopefully do is make him realize the path he was on. To understand what an emotional affair is, and how it develops.
To use a comparison: It’s like an intervention where you might convince a teenage child that occasionally taking e or oxy is not "innocent" because it’s only once (or once a month) and it’s controllable, because it’s a lot more likely to get him in trouble and become an addiction.