We’ve created a view only link to share with our external clients so they can see what tasks are in progress.
The problem is, when they click on the created link on a mobile device, they get a message that it can only be viewed on desktop.
Is there no option for them to view on a mobile device at all?
I do not believe has this capability at the time, but hopefully, it is something they can implement in the future!
I just came across this as well… cue sad trombones
Another roadblock in the Asana journey as I try to use it company wide… Google Sheets it is I guess…
Really disheartening when what feels like basic functionality seems to be lacking 
OK - not only is it not supported on mobile, but when you do finally view it read only on desktop, its more of an advertisement than an actual viewable document… the recipient cant even view task details or subtasks!! Not just a broken feature, but one that I nearly sent out and would have caused a negative impression! Yikes!
