An alternative is to extract the .Data slot from the S4 object with @. The code below will produce the same result as the code provided by Jari Oksanen.

library(phyloseq)
library(vegan)

data("GlobalPatterns")

GlobalPatterns %>% 
otu_table() %>%
`@`(., ".Data") %>% 
t() %>% 
vegan::rarecurve(.,step = 10000)