We present measurements of the real diagonal microwave conductivity of the reentrant insulating quantum Hall phases in the first excited Landau level at temperatures below 50 mK. A resonance is detected around filling factor $ u=2.58$ and weaker frequency dependence is seen at $ u=2.42$ and 2.28. These measurements are consistent with the formation of a bubble phase crystal centered around these $ u$ at very low temperatures.
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