Use an explicit is phoneme type constant to specify the type-based conditions.

src/libespeak-ng/compiledata.c

 };
 
 static keywtab_t k_properties[] = {
-	{ "isPause",      0, phPAUSE },
-	{ "isVowel",      0, phVOWEL },
-	{ "isNasal",      0, phNASAL },
-	{ "isLiquid",     0, phLIQUID },
-	{ "isUStop",      0, phSTOP },
-	{ "isVStop",      0, phVSTOP },
-	{ "isVFricative", 0, phVFRICATIVE },
+	{ "isPause",      0, CONDITION_IS_PHONEME_TYPE | phPAUSE },
+	{ "isVowel",      0, CONDITION_IS_PHONEME_TYPE | phVOWEL },
+	{ "isNasal",      0, CONDITION_IS_PHONEME_TYPE | phNASAL },
+	{ "isLiquid",     0, CONDITION_IS_PHONEME_TYPE | phLIQUID },
+	{ "isUStop",      0, CONDITION_IS_PHONEME_TYPE | phSTOP },
+	{ "isVStop",      0, CONDITION_IS_PHONEME_TYPE | phVSTOP },
+	{ "isVFricative", 0, CONDITION_IS_PHONEME_TYPE | phVFRICATIVE },
 
 	{ "isPalatal",  0, CONDITION_IS_PHFLAG_SET | phFLAGBIT_PALATAL },
 	{ "isLong",     0, CONDITION_IS_PHFLAG_SET | phFLAGBIT_LONG },

src/libespeak-ng/synthdata.c

 
 		switch (instn & 0xe0)
 		{
-		case 0x00:
+		case CONDITION_IS_PHONEME_TYPE:
 			// phoneme type, vowel, nasal, fricative, etc
 			return ph->type == data;
 		case 0x20:

src/libespeak-ng/synthesize.h

 // place of articulation
 #define i_isVel      0x28
 
-#define CONDITION_IS_PHFLAG_SET 0x40
+#define CONDITION_IS_PHONEME_TYPE 0x00
+#define CONDITION_IS_PHFLAG_SET   0x40
 
 #define i_StressLevel  0x800