This is a current limitation that should be addressed.
I have the same issue, even if you could specify a phase in a column on the Project Schedule, would be a big help for allocating tasks/time to my team members.
Being able to report on time recorded in phases would be a big win for me.
I am shocked allocations in phases don't sync into smartsheet projects from resource management. Between that and not being able to allocate multiple people to one task, this is not a very sophisticated system.
The other way around is also a shortcoming...considering that one typically starts with the creation of a project in Smartsheet, one should be able to allocate each task to a Phase, such that the work items are then created inside their relevant phase in Resource Manager when one creates the RM project from Smartsheet.
I would go as far as saying that the integration between Smartsheet and Resource Management is unfit for purpose without this functionality.
The big problem here is that Resource Management has no concept of billable and non-billable time. The result is that Smartsheet's own advice was "Create two phases. One called billable and one called non-billable and set the billing rates differently on each one." Then I find you don't support it in Smartsheet.
I have to be honest. This functionality was sold to us and I'm extremely dissapointed it's not there.
I'll go a step further. When setting up the integration between Smartsheet and Resource Management we're asked to map columns for "Assignee" and "% Allocation". We should also have mapping fields for "Phase" and "Category". as a bare minimum. An even better system would be that the tasks we create are carried over into Resource Management and that users can code time against each task.
I want to be able to look at my teams project plans, understand what tasks were allocated to them, how much time was estimated and how much time was required. This is basic functionality needed for understanding Earned Value.