Auto-populate child reference field based on parent table criteria

I have a parent table Phases where each record is a specific project phase and has a Start Date-Time and End Date-Time and do not overlap for a given project (fields of Phases table = project ID, phase name, start date-time, end date-time)
I have a child table Time Log where there are many time log entries (records) for each project and each record has a start date-time and end date-time)

I am trying to associate each time log record with the correct Phase based on the start and end date-time of the time log record with the start and end date-time of the Phases

Any tips or guidance would be much appreciated! I have seen some suggestions to using a formula reference field (not sure how that works) and automations (I tried that and am having some issues). I would prefer not to use automations but if thats the only way then so be it. Thanks!

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Nick Mesec
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