How many number of apple IDs can be created for free in a single iPhone device?

There is no limit on the number of apple IDs you can create and use in a  single iPhone device.

Multiple apple IDs are preferred by people who use multiple email ids (e.g: one apple id for all job related work and one for your personal use) or international users who wish to switch between multiple Apple ID’s set to different countries so that they can access different features and app store content.

Having multiple ids does have some disadvantages though:

• It gets difficult to keep track of your content and purchases.
• Changing an Apple ID on a device that is using it can possibly cause unexpected issues with iOS and conflicts with some apps. For example, if you own an app on one Apple ID but not the one being changed to, or if you’re logged into an Apple ID that has Game Center details associated with it and the new one doesn’t. Thus, you’ll generally only want to do this on a device that has been freshly reset to factory default settings or on one without any critical App Store and related downloads tied to it.
• In the future if you want to continue with only one Apple ID, Apple does not allow you to consolidate two Apple IDs, so you will have to delete one of your apple IDs which may result in losing purchased apps, movies, TV shows and books.

If more than 1 member of your family is using an apple device i suggest you use Apple's Family Sharing. Family Sharing makes it easy for up to six people in your family to share each other’s iTunes, iBooks, and App Store purchases without sharing accounts.