Dysarthria due to Amyotrophic Lateral Sclerosis (ALS) progressively distorts the acoustic space affecting the discriminability of different vowels and fricatives. However, the extent to which this happens with increasing severity is not thoroughly investigated. In this work, we perform automatic 4-class vowel (/a/, /i/, /o/, /u/) and 3-class fricative (/s/, /sh/, /f/) classification at varied severity levels and compare the performances with those from manual classification (through listening tests). Experiments with speech data from 119 ALS and 40 healthy subjects suggest that the manual and automatic classification accuracies reduce with an increase in dysarthria severity reaching 59.22% and 61.67% for vowels and 41.78% and 38.00% for fricatives, respectively, at the most severe cases. While manual classification is better than automatic one for all severity levels except the highest severity case for vowels, the difference between the two gradually reduces with an increase in severity.