What’s the explanation for picking up a ringing phone if the person who owns the phone, is away from their desk?
They caller isn’t calling you, you can’t help. Leave it alone.
The recipient may have set up call forwarding, or a usefull voicemail, which the caller now won’t receive.
More than that - you’re wasting your own time (picking up a call you can’t help with), the callers time (probably needing to call back, wondering who they just spoke to) and introducing uncertainty (will the message you took even get to the recipient?).
Hey, you - leave that phone alone.