Answer:
For teaching the short /e/ sound, some suitable keywords for a sound-symbol card could be:
Egg
Elephant
Exit
Envelope
Elf
For teaching the short /i/ sound, some suitable keywords for a sound-symbol card could be:
Ink
Igloo
Itch
Insect
Imp
For teaching the /ĕ/ sound, some suitable keywords for a sound-symbol card could be:
Ed
End
Ent
Ebb
Egg
Since "echo" is not a good keyword for any of these sounds, I would suggest selecting a different keyword based on the specific sound you want to teach.