One of the main parameters by which the Earth differs at all from most of the cosmic bodies is atmospheric pressure. On Mars it is not zero because it has a visible atmosphere, but still far below the usual for us: about 0.6 percent of the earth’s or 600 Pascals. Low pressure may affect the smartphone in several ways.
Some of the factors are fairly obvious, but not critical. For example, when low density of the air microphone and speaker will probably continue to work, but to receive and reproduce the sounds they are inefficient — that is, the speaker will sound quieter.
But pressure can affect critical components such as the battery. In 2012, NASA conducted a test of lithium-ion batteries under low pressure, and one of the “experimental” turned out to be the battery of the iPad, which is not much different from the batteries of smartphones. It turned out that it is blown up, and although when the pressure returns to normal, but being at low pressure for several hours reduces the capacity by about a third. So the smartphone on Mars will have to charge more often.