Short answer: Conversion turns the group coverage into an individual permanent policy at individual rates, with no health questions, and Texas law requires every group life policy to offer it. Portability, where the contract includes it, lets the person keep term coverage at group-style rates; it is usually cheaper but has conditions set by the carrier.
Conversion is a legal right in Texas: within 31 days after employment ends the person can buy an individual non-term policy, without evidence of insurability, for up to the amount that ended, at the insurer’s customary individual rates.
Portability is a contract feature, not a statutory right. When offered, it typically continues term coverage, often through a separate portability policy, at rates closer to group rates. Carriers commonly limit it, for example to people below a stated age, who are not disabled, and who apply within a short window, and the ported amount may have its own maximum. Check the certificate.
A practical rule: a healthy person usually saves money by porting or buying new individual term; someone with health problems may be better served by converting, because conversion cannot be declined. Some people use both, porting part and converting the rest, where the contract allows.