Does DEX mod apply to Ranged Spell Attacks?

No. Ranged weapon attacks use Dexterity as their ability modifier. When you cast a spell that requires an attack roll (note: most don't) you're not making a weapon attack.

PHB page 194, Attack Rolls > Modifiers to the roll > Ability Modifier:

[...] Some spells also require an attack roll. The ability modifier used for a spell attack depends on the spellcasting ability of the spellcaster, as explained in chapter 10.

PHB page 205, Attack Rolls:

[...] Your attack bonus with a spell attack equals your spellcasting ability modifier + your proficency bonus.

Long story short: as a Cleric your cleric spells with attack rolls will add your Wisdom mod bonus, not your Dexterity bonus, regardless of whether they are ranged spell attacks or melee spell attacks.

Separately, if your Cleric were to take the Mage Initiate feat to gain access to spells from the spell lists of other classes, you would have to use that class's spellcasting ability modifier.