French etymology is not very phonetic. The reason is that it's based on old French, spoken from the 9th to 14th centuries. The pronunciation of French has changed significantly since this period.
Here are ten words which reflect the difference between spelling and pronunciation in French:
mot (word) the t is silent
sept (seven) the p is silent
vous (you) the s is silent
fils (son) the l is silent
samedi (Saturday) the e is silent
bras (arm) the s is silent
pied (foot) the d is silent
doigt (finger) the g and t are silent
oeufs (eggs) the f and s are silent
haricot (bean) the h and t are silent
From the examples, we can see that French spelling has many silent letters. They were pronounced in Old French but not today. Thus French spelling reflects the changes in pronunciation which the language has undergone over time.