Answer: Clover is one of those weeds that is extremely difficult to control, even with chemicals. Any broadleaf weed killer used in your bed of phlox will be more detrimental to the phlox than to the clover. Probably the best course of action is to dig the bed, separate the clover from the phlox, remove all the clover roots, and replant the phlox. It's time consuming and labor intensive, but once the bed has been thoroughly renovated, you should be able to keep ahead of any newly sprouting clover plants by pulling them up before they flower and set seed.
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