library(magrittr)

def_text <- fp_text(color = "black", italic = FALSE, font.size = 20)

lastPhId <- function(presentation) {
  index = presentation$cursor
  x <- slide_summary(presentation, index = index)
  x <- x[x$type == "body", ]
  max(as.numeric(x$id))
}

TITLE = fpar(ftext("My Title", prop = def_text))
TITLE <- update(TITLE, fp_p = fp_par(text.align = "left"))

doc <- read_pptx()
doc %<>% add_slide(layout = "Title and Content", master = "Office Theme")
doc %<>% ph_empty_at(left = 3, top = 3, height = 1, width = 4, bg = "yellow")
doc %<>% ph_add_fpar(value = TITLE, id_chr = lastPhId(doc))

print(doc, target = "ph_add_fpar.pptx")
system("cmd.exe", input = "ph_add_fpar.pptx")