The cruise phase begins when the third stage of the Delta ll rocket separates and ends when the spacecraft is 45 days from entry into the Martian atmosphere. Solar panels on the cruise stage will provide electricity for the spacecraft.
Both spacecrafts use a cruise low-gain antenna (CLGA) for early cruise communications i.e. when the spacecraft is close to earth. After a first few months of cruising, the spacecraft will switch to a medium-gain antenna (MGA) for communications during the rest of cruise i.e. when the spacecraft is more than a certain distance from the earth.
In short, during this phase, the parts of the spacecraft are checked and maintenance is done, the spacecraft and subsystems are monitored, altitude correction, navigation activities, trajectory correction maneuvers and preparation for entry descent, landing and surface operations is also done.