Hi Ivan,
There is definitely some CSS instruction (probably from OutSystems UI since you don't mention having done anything in that sense) which is promoting this behavior and you need to override it.
You can easily check this with Chrome Developer Tools (F12 on browser) and check the table Elements.

You can then select the element and see on the Styles tab the CSS being applied where you can uncheck them or change them (see image above) and find out which one is causing the behavior, find out what is the change you need to make and include it on the default Theme to override this behavior.
Alternatively, you can use Columns2, Columns3 (and other) widgets from OutSystemsUI which help you place the content side by side and define how they break in Phone:

Regards,
João