The LRI assessment would be best to assess phonemic awareness. It assess preschool-second grade. This assessment could also be used before preschool aged children to figure out where the student is with their skills with phonemic awareness. Below is the link for LRI where you can find the assessments and the scoring sheets. Reading A-Z would also be another good assessment you could use to assess phonemic awareness.
http://www.literacyresourcesinc.com/resources/assessments/
Reading A-Z Phonemic Awareness
http://www.literacyresourcesinc.com/resources/assessments/
Reading A-Z Phonemic Awareness