If you work on the basis of phone tips being OK long term and making 10% profit on turnover, which is very good, consider this:

If you pay $11 a tip you need to bet $110 a selection just to cover your phone costs.

If you pay $22 a tip you need to bet $220 a selection just to cover your phone costs.

If you pay $33 a tip you need to bet $330 a selection just to cover your phone costs.

Remember noone makes phenomenal profits on turnover long term from punting on horses.
I think this should make things pretty clear if you are going to pay per selection.

Mr. Logic