I was redirected to another flight due to leaving my phone in the terminal after boarding. I knew where my phone was. I approached staff right away as we were still boarding. Manager & attendant were rude & insensitive on the matter w/ an attitudes questioning were my phone was. I explained the location & she went “LOOKING” for it & returned back in literally 2 secs after stating she couldn’t find it. Following that interaction, Manager & attendant states: “Oh well, the plan needs to leave! Not gonna be late!” I was told to grab my belongs, in hope to grab my phone & board the plane. Once I did, the cabin door was shut & I was left in the terminal confused on how was I getting to my final destination Key West. w/o any communication w/ my partner I was traveling w/ left on the plan. - I was giving “stand by” boarding pass onto the next flight to Dallas. - However, my finally destination was Key West, Florida. I questioned the helpful agent at the gate, where is my connection flight to Key West from Dallas? - i can see the frustration on her face yet w/ a smile assisted w/ the problem the last crew failed to help with. I don’t have the means to travel AA again after this experience! I will exhausting all my options before boarding another AA flight. I work in customer service & to be treated this way is unacceptable. Especially if traveling w/ someone & no commutation was made w/ either party on what next step to take or if the other is in ok etc.