Phelan, a Beaumont Republican, had previously insisted he had enough votes to thwart a challenge from the right led by state Rep. David Cook of Mansfield.
The two-term Republican caught many Capitol observers off guard when he emerged as the standard-bearer for a coalition that wants to depose Phelan and reshape how the House operates.
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Four GOP state representatives suspended their bids to challenge Phelan and 48 Republicans backed Cook, which could threaten Phelan’s shot at a third term.
Reps. Tom Oliverson and Shelby Slawson, both members of House Republican leadership, became the first two candidates to challenge Phelan’s speakership.