Dual-function radar-communication (DFRC) technology plays a crucial role in unmanned aerial vehicle systems. Waveform diversity of multiple-input multiple-output (MIMO) technology with beamforming of phased array can simultaneously achieve main-lobe detection and side-lobe communication through the beampattern modulation. However, traditional solutions lack multi-user communication capabilities in the same direction. To address this issue, we propose a transmit beamforming method for the MIMO DFRC system with the phased array. Firstly, we design orthogonal sequences to encode the multi-user communication symbols and introduce the encoded information into the sidelobes of transmitted beampatterns. Secondly, the beamforming optimization model is constructed to minimize the integrated sidelobe levels with information embedding and mainlobe similarity as constraints. Finally, the proposed non-convex optimization problem is solved by the block coordinate descent algorithm. The simulation results show that the proposed method can achieve reliable communication among multiple users without detection performance loss.