everything is pretty much in the title, if somebody could explain why this sentences lack article / have this famous "zero article". Best Regards, Marcello
In what follows I refer to the Nueva Gramática de la Lengua Española (NGLE, §15.6). In general, nouns without articles, demonstratives and such are said to be undetermined. Undetermined nouns are to be interpreted as non-specific, that is, not referring to specific items, but generally to types or classes. They also appear often in stereotypical or prototypical situations.
The NGLE notes that singular undetermined nouns are common in idioms and in other expressions which show social stereotypes associated with people or things. This and the idea that they represent classes rather than specific objects is the reason why they often form units with verbs, as in “tener miedo”, “llevar sombrero”, “buscar pareja”, etc. “Tener miedo” is actually explainable by the fact that it's a non-count noun (although Spanish is more flexible than English in this regard), and such nouns commonly appear without an article when they're objects of verbs. “Hacer pie” is somewhat different because, although it has the same structure, it's actually an idiom (it doesn't directly have to do with a foot; rather it means “to be able to touch the bottom of a water mass with your feet while your head stays above water”), but it makes sense that this general situation is expressed with an undetermined noun. The other two examples use count nouns that, without an article, are to be interpreted as typical representatives of a class.
«Tengo miedo a perder pie» means being afraid of losing your foothold, of not putting a foot on the ground because it's unstable, e.g. a weak part of the floor or when you look at the ice, scared you'd fall. Another explanation may be that someone lost their bearings, got confused or lost its way.
«Tengo miedo a perder el pie» refers to when people are living in fear of losing their feet due to diabetes, ulcers or as the result of an accident or injury.
«Le tengo rabia al silencio" = I hate silence, rage against the... «El» is a definite article, if «a» is followed by «el», the two words become «al». It doesn't make sense without «el» in Spanish.
"Tengo la rabia," meaning "I have rabies," which is a disease.
'Tener' is one of the verbs of feelings that requires a noun(tengo+noun). In «Tengo el miedo» the article «el» incarnates/embodies 'the fear' as «al» to 'silence' in «Le tengo rabia al silencio».