I work in a small office where each of has our own set of clients that we have established relationships with over the years. I've recently moved desks and am now sitting almost side by side with another sales person who takes pride in having the highest commissions each month.
For the past few weeks, since sitting near this person, my clients have started disappearing. When I call to service their accounts and leave a VM, during a follow up call I find out that this other sales person has gone around me to contact them and complete the sale. The first time, they said that I wasn't at my desk and the client was in a hurry so I brushed it off as an anomaly. But it has now happened at least 3 times. I assume the person is getting this information while I'm on the phone since my computer is locked when I am away from my desk. Our manager just sees it as friendly competition so not too much help there.
I'd like assistance on how I might start a conversation with my co-worker that doesn't dive into them getting defensive or me accusing. However, I'd also like to try and make it clear that they need to stop this behavior. Any thoughts on how I can approach this conversation?