XLR has a distinct advantage over two-wire “phone” connections which you lose with an adapter. XLR, balanced, 3 wire microphones and cables are preferred where possible.
XLR is what is called a “balanced” input while a “phone plug” or mini is unbalanced. For short distances the difference is usually inconsequential, but in electrically noisy areas or for longer length cables connections that are not balanced can add noise to your track. Adapting from unbalanced (two wire or phone connectors) to XLR does not solve the problem because you are converting the balanced connection to unbalanced thereby defeating the advantages of the XLR connection.
Another advantage to the XLR is in the use of remote powered or “phantom” powered microphones which receive constant power from the camera rather than from batteries in the microphone.
XLR or balanced cables have three conductors where unbalanced cables have only two. The wiring of the XLR connection is designed to cancel out electrical noise, which has to do with the “Balanced” designation. In a balanced connection the two signal cables are equal and opposite with relation to the third connection which is ground. Electrical noise which may enter the cable is canceled out with respect to ground providing a clean signal at the other end. Electrical noise which is radiated into an unbalance cable is simply added to the audio signal on the cable.
You’ll sometimes hear old-timers refer to the XLR as a “Cannon” connector, which refers to the original manufacturer, Cannon Electric, which was founded by James H. Cannon. The name has no relation to the Canon (one “n”) cameras which may feature this type of connector.
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