It depends totally on your personal circumstances and who the endowment policy is with - I too have two endowments with Phoenix and can't even get an offer from one of these companies who offer to buy them - so will hang on to them for another 4 years until they mature - at least I will get a terminal bonus
You should look in to FREEZING the payments - you then get to stop paying the monthly installments - but get to keep some of the bonus - how much is the question - can anyone advise ?