Map and Reduce phases will run on multiple queues. If you do not have a SuiteCloud Plus license, you get only two queues. With 1 SC+ license, you'd have up to five queues available, which you can see under details. The Get Input Data and Summarize phases only run once per Map/Reduce script execution, regardless of the number of queues you have available. If you want to change the number of queues used for the Map and Reduce phases, you can change the concurrency setting of the script deployment.

@scottvonduhn Thank you for your reply. As per Concurrencey limit field help on map/reduce deployment record: Use this field to set the number of processors available to the deployment. This value equates to the number of jobs submitted for the map and reduce stages. So if concurrency limit is set to 5, it means 5 map jobs and 5 reduce jobs are submitted to be processed by 5 processors. If getInputdata returns an array of 40 key and their values then 5 of the keys and their values will be submitted to either map or reduce stage at once to be processed by 5 processors and as soon as one (key, pair) is processed, map or reduce will pick up 35th key value pair.