Husband getting close to another girl?

Husband (31) has a friend at work (F22) who he’s gotten pretty close to. Hes even met her bf. Their work is mobile so in order for them to talk they have to meet up, instead she often calls him apparently asking him for help on certain things although I’ve noticed their calls are getting longer and longer. He’s swore up and down she’s just a coworker, he would never do anything to mess up our relationship/ family (together for 10years, 2 kids together) they say they just talk about work stuff and she will ask him for advice on how to go about certain things at work, she apparently knows all about me even invited us to her bfs birthday party. Should I be worried about their long phone calls? Last call was 24 minutes…. He doesn’t delete them cause he says he has nothing to hide. The only texts he has from her are the texts from a work group chat she is in.

To make things short: should I be worried about my husband speaking to another woman on the phone for extended periods of time?