When I was an IT manager, I never answered my phone if I was talking to someone, and especially if they were one of my team (unless it was the incident response desk which would mean they were escalating a critical problem).

I had constant looks of surprise that I would let calls go to voicemail, even if it was my boss. The feedback I would often get later (via 360 reviews, or even just during casual conversation) was that it was a huge positive tick in their opinion of me as a manager (and person). They felt they were being listened to and that I was paying attention to them.

I remember reading an etiquette guide once where 'proximity' (temporal and spatial) should be the deciding factor in prioritizing your attention. Someone standing in front of you is closer than a phone call or an email - that should always be #1 (and phone > chat > email). It's generally what I try to follow.