The correct spelling of the phrase "was source strength" is /wəz/ /sɔrs/ /streŋθ/. The initial sound is represented by the letter "w" which is pronounced as the voiced labio-velar approximant /w/. The next word "source" is spelled as /sɔrs/ which starts with the voiceless alveolar fricative /s/ sound followed by the voiced alveolar sibilant /z/ sound. The final word "strength" is spelled as /streŋθ/ which contains the voiced velar nasal /ŋ/ sound followed by the voiceless dental fricative /θ/ sound.