If the Safari browser on your iPhone is set to block cookies, you will have problems logging into the SmartMLS site.
You will see the following screens if cookies are blocked:
To configure Safari not to block cookies on your iPhone, go to Settings, scroll down and tap on Safari.
Then scroll down to the Privacy & Security section and move the Block All Cookies slider bar to the off position (left):
You should now be able to log into SmartMLS on your iPhone.