In the parent table, create a summary field that captures Max Date. If you do not have a parent table, you may have to create one in order to find the max date. Could you not filter your report to sort in descending order by that date?
If you want to find the maximum phase, you'd make another max summary field based on the max date summary field. See configuration for new summary field below.
Field to summarize: Choose a field from the "table name" table -
[Phase] << field to summarize
Where the following is true:
[Date Field] = the value in the field [Max Date Field] <your max date summary field.
See how that works for you.
In your [max date] summary field, go into the properties and add a condition to "only summarize where the following is true". Select your [phase field] is equal to 5.
You will derive the highest date where phase is 5.