You can use Microsoft Excel for iPhone and iPad for free for viewing, creating, and editing spreadsheets without Office 365 subscription. The app now has the same capabilities on your iPhone and iPad.
You can use Excel for iPhone and iPad to view your spreadsheets (XLS, XLSX) the exactly as on the desktop version of Word. You can save your Office documents in the online storage services OneDrive and Dropbox. In addition to Excel, Word and PowerPoint are free for iPhone and iPad as well. An Office 365 subscription is required for advanced features, but most home users can work very well with the free version.