All websites should be compatible with mobile phones and tablets and there are a number of ways to do this. Some businesses have a mobile version of the website created, the site will automatically detect if you are using a mobile device and often switch you to the mobile version. You may opt for an app to be built for you to allow your users access to a more mobile based version of your site, if you do this you should still ensure that your main website is compatible too.
There are a large number of people using their mobile devices to view websites and this number is growing year upon year. You need to ensure that you are checking the statistics for your mobile version of the site to see if there are any pages that have a particularly high bounce rate. If they do then you may need to revisit that page and check it is displaying correctly and functioning as it should.